PSMB4 overexpression enhances the cell growth and viability of breast cancer cells leading to a poor prognosis.

PSMB4, proteasome subunit β4, is a member of the ubiquitin-proteasome family, and is elevated in a variety of malignancies. However, the expression level and related mechanism of PSMB4 in breast cancer remains unclear. Therefore, the present study investigated the expression level of PSMB4 in eight pairs of breast cancer and adjacent normal tissues. In addition, the relationship between the expression of PSMB4 and the clinical data of 92 breast cancer patients was discussed. First, it was found that PSMB4 expression was obviously upregulated in breast cancer tumor tissues and cell lines (MDA-MB-231 and MCF-7), and its level was significantly associated with tumor grade (P=0.005), tumor size (P=0.047), Ki-67 expression (P=0.040) and the poor prognosis of breast cancer. The present results demonstrated that PSMB4 could promote the proliferation of breast cancer cells, and was positively correlated with the expression of PCNA using an in vitro starvation-refeeding experiment. In addition, PSMB4‑siRNA transfection assay suggested that PSMB4 knockdown can decrease NF-κB activity and cell viability, and result in cell cycle arrest at the G1/S phase. These findings revealed that PSMB4 might facilitate breast cancer progression by promoting cell proliferation and viability. In summary, PSMB4 may be recognized as an efficacious prognostic marker and potential therapeutic target for breast cancer.